Flow additive for urethane system

This invention relates generally to a flow additive for a urethane system which can be coated onto a substrate to produce a substantially uniform coating of adhesive.

Flow additives for two-component urethane systems are well known. For example, MODAFLOW flow additives are used for this purpose and are known to contain polymerized residues only of (meth)acrylic acids and alkyl esters. However, there is a need for alternative flow additives which have improved properties.

The present invention is directed to a method for improving flow of a two-component urethane system by adding a hydroxy-functional acrylic polymer.

All percentages are weight percentages, and all temperatures are in ° C., unless otherwise indicated. Percentages of monomer residues are on a solids basis, i.e., excluding solvents. A “hydroxy-functional acrylic polymer” is a polymer having at least one hydroxyl group per polymer chain, wherein the hydroxyl group is attached to an aliphatic carbon atom, and wherein the polymer comprises at least 60 wt % polymerized monomer residues of acrylic monomers, e.g., (meth)acrylic acid, alkyl and/or hydroxyalkyl(meth)acrylates, preferably at least 70 wt %, preferably at least 80 wt %, preferably at least 90 wt %, preferably at least 95 wt %. “(Meth)acrylic” refers to either acrylic or methacrylic. Hydroxy-functional acrylic polymers may also contain polymerized residues of monomers other than those listed above, e.g., styrene, vinyl esters, (meth)acrylamides, etc. “Phthalic acid” refers to benzene-1,2-dicarboxylic acid. Polymerized residues of phthalic acid may be the result of using either phthalic acid or phthalic anhydride as a starting material in preparation of the hydroxy-terminated polyester polyol. “Aliphatic acids” are dicarboxylic acids having no aromatic rings, e.g., adipic acid, azelaic acid, glutaric acid and succinic acid. “Toluene diisocyanate” refers to the commercial product sold under this name, which is predominantly the 2,4-isomer, with small amounts of the 2,6-isomer, and possibly other isomers.

Preferably, the hydroxy-functional acrylic polymer has M n from 5,000 to 70,000; preferably M n is at least 6,000, preferably at least 7,000, preferably at least 8,000; preferably M n is no greater than 60,000, preferably no greater than 50,000, preferably no greater than 40,000, preferably no greater than 30,000, preferably no greater than 20,000, preferably no greater than 15,000. Preferably, the hydroxyl-containing monomer is from 10 to 50 mole % of the acrylic polymer; preferably at least 12 mole %, preferably at least 15 mole %; preferably no greater than 30 mole %, preferably no greater than 25 mole %. Preferably, the hydroxyl-containing monomer is a hydroxyalkyl(meth)acrylate, preferably a C 2 -C 8 hydroxyalkyl(meth)acrylate, preferably a C 2 -C 4 hydroxyalkyl(meth)acrylate, preferably a C 2 -C 3 hydroxyalkyl(meth)acrylate. Preferably, the amount of the hydroxy-functional acrylic polymer in the combined components of the urethane system is from 0.01 to 5 wt %; preferably at least 0.1 wt %, preferably at least 0.3 wt %, preferably at least 0.5 wt %; preferably no more than 3 wt %, preferably no more than 2 wt %, preferably no more than 1.5 wt %, preferably no more than 1 wt %.

Preferably, the two-component urethane system comprises: (a) a hydroxy-terminated polyester polyol; and (b) an isocyanate-terminated prepolymer comprising polymerized residues of at least one of diphenyl methane diisocyanate and toluene diisocyanate, and a glycol or polyol. Preferably, the glycol or polyol has M n , from 90 to 1000. Preferably, the hydroxy-terminated polyester polyol comprises polymerized residues of: (i) phthalic acid and (ii) an aliphatic diol having M n , from 60 to 150; wherein the hydroxy-terminated polyester polyol has a hydroxyl number from 15 to 60 mg KOH/g. Preferably, the hydroxy-terminated polyester polyol has no more than 15 wt % polymerized residues of aliphatic acids.

Preferably, the hydroxy-terminated polyester polyol contains polymerized and esterified residues of phthalic acid and an aliphatic diol; it may also contain other di-acids and diols. Preferably, a hydroxy-terminated polyester polyol has no more than 10 wt % polymerized residues of aliphatic acids, preferably no more than 5 wt %, preferably no more than 3 wt %. The aliphatic diol may be an α,ω-dihydroxy alkane or an ethylene or propylene glycol oligomer. Preferred aliphatic diols include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol and triethylene glycol. Especially preferred aliphatic diols include diethylene glycol and 1,6-hexanediol. Preferably, the aliphatic diol has M n , from 90 to 150, preferably from 90 to 130, preferably from 100 to 125. The hydroxy-terminated polyester polyol is a hydroxy-terminated polyester, preferably with a hydroxyl number from 15 to 55 mg KOH/g, preferably from 20 to 50, preferably from 22 to 35. Preferably, the hydroxy-terminated polyester polyol contains from 40% to 75% polymerized residues of phthalic acid; preferably at least 45%, preferably at least 48%, preferably at least 50%, preferably at least 52%; preferably no more than 70%, preferably no more than 65%, preferably no more than 63%, preferably no more than 61%, preferably no more than 59%. Other isomers of phthalic acid (e.g., isophthalic acid or terephtahalic acid) may also be used to make the hydroxy-terminated polyester polyol, but preferably these other isomers are no more than 20 wt % of the total weight of di-acids, preferably no more than 15 wt %, preferably no more than 10 wt %, preferably no more than 7 wt %, preferably no more than 5 wt %. Preferably, the hydroxy-terminated polyester polyol contains from 25% to 60% polymerized residues of an aliphatic diol having M n , from 60 to 150; preferably at least 30%, preferably at least 35%, preferably at least 37%, preferably at least 39%; preferably no more than 55%, preferably no more than 52%, preferably no more than 50%, preferably no more than 48%. Small amounts of residues of compounds with more than three hydroxy groups may be present to increase branching, e.g., pentaerythritol. Preferably, the amount of residues of compounds with more than three hydroxy groups is no more than 5% of the total amount of diol(s), preferably no more than 2%, preferably no more than 1%, preferably no more than 0.5%, preferably no more than 0.2%, preferably no more than 0.1%. Suitable triols include, e.g., glycerol, trimethylol ethane, trimethylol propane and castor oil. The amount of diols, triols, and tetra-ols added is sufficient to react with all of the carboxyl functionalities and to result in a polyol with a hydroxyl number from 15 to 60 mg KOH/g. This amount can be calculated easily from the amounts of other ingredients.

Preferably, the hydroxy-terminated polyester polyol is produced by the steps allowing phthalic anhydride (or phthalic acid) to react with the aliphatic diol at a temperature from 150° C. to 260° C. Preferably, the reaction temperature is from 150° C. to 240° C., preferably from 170° C. to 235° C., preferably from 180° C. to 230° C. Preferably, the reaction pressure is about atmospheric pressure (about 100 kPa), although reduced pressure may be used to assist in removing water formed in the esterification reaction. Preferably, the reaction mixture is heated first to about 100-130° C., followed by heating to the indicated reaction temperature to remove water. Reaction times of course will vary with the other conditions, and can be determined easily by one skilled in the art, but typically are in the range from 5 hours to 30 hours, preferably from 12 to 25 hours. Preferably, an esterification/transesterification catalyst is present in an amount no more than 0.2 wt %, preferably no more than 0.05 wt %. These catalysts are well known in the art and include tin, titanium, bismuth and zirconium catalysts. Tin catalysts are preferred, especially alkyltin tris-alkanoates and hydroxybutyl tin oxide, but titanates, e.g., tetra-alkoxy titanates or bismuth alkanoates or mixtures thereof may also be used.

Preferably, the glycol or polyol having M n , from 90 to 1000 which is incorporated into the isocyanate terminated prepolymer has two to three hydroxyl groups per molecule. Preferably, the glycol or polyol has M n , from 150 to 800, preferably at least 250, preferably at least 300; preferably no more than 700, preferably no more than 600. Preferably, the polyol is a polyether or polyester polyol, preferably a polyether polyol. Preferably, the isocyanate-terminated prepolymer comprises polymerized residues of: (i) 50 to 85 wt % of at least one of MDI and TDI; and (ii) 15 to 50 wt % of a glycol or polyol having M n , from 90 to 1000; preferably at least 55 wt % MDI/TDI and no more than 45 wt % glycol or polyol, preferably at least 60 wt % MDI/TDI and no more than 40 wt % glycol or polyol, preferably at least 65 wt % MDI/TDI and no more than 35 wt % glycol or polyol, preferably no more than 80 wt % MDI/TDI and at least 20 wt % glycol or polyol.

The isocyanate-terminated prepolymer has polymerized residues of MDI and/or TDI. Other difunctional isocyanates may be present, e.g., an aliphatic diisocyanate, e.g., hexamethylene diisocyanate. MDI may be a mixture of 4,4′ and 2,4′ isomers. Preferably, at least 80 wt % of the polymerized residues of isocyanates in the isocyanate-terminated prepolymer are from MDI and TDI, preferably at least 85 wt %, preferably at least 90 wt %, preferably at least 95 wt %. Preferably, at least 50 wt % of the MDI residues are from the 4,4′ isomer, preferably at least 70 wt %, preferably at least 80 wt %, preferably at least 90 wt %, preferably at least 95 wt %. The difunctional aromatic isocyanate is mixed with a polyol to form the isocyanate-terminated prepolymer. In some embodiments of the invention, the polyol mixed into the isocyanate component is at least one difunctional or trifunctional polymer of ethylene oxide, propylene oxide or a combination thereof. Preferably, the isocyanate-terminated prepolymer has an isocyanate content from 7% to 21%, more preferably from 11% to 15%.

In the two-component urethane system, the relative proportions of isocyanate groups to isocyanate-reactive groups may vary as desired, preferably within a molar ratio of NCO/OH groups of 0.9:1 to 2:1. Preferably, the NCO/OH group molar ratio is from 1:1 to 1.8:1, alternatively from 1.1:1 to 1.6:1, alternatively from 1.2:1 to 1.4:1.

Preferably, the components of the two-component urethane system are diluted with solvent prior to coating onto a substrate. As the term is used herein, a solvent is a substance which is liquid at 25° C. and has a boiling point at atmospheric pressure of no more than 100° C. Preferably, the combined components of the system as applied to the substrate contain from 45-60 wt % solids, preferably from 46-57 wt %, preferably from 47-55 wt %, preferably from 48-53 wt %. Suitable solvents include ethyl acetate, methyl acetate and methyl ethyl ketone. Ethyl acetate is especially preferred.

The two components of the urethane system preferably are mixed using a suitable mixer (e.g., an electrically, pneumatically, or an otherwise powered mechanical mixer, or a static mixer) prior to or during application to a substrate to form the bonding agent. Thus, the isocyanate component typically will be packaged separately from the polyol component. Mixing may take place at any suitable time prior to the laminating process. All of the present steps may be carried out under ambient room temperature or supra-ambient conditions. For example, the two components may be heated just prior to mixing and applied at elevated temperature during the coating and lamination process. Preferably, the temperature does not exceed 65° C. As desired, heating or cooling may be applied to the resulting laminate. Preferably, a gravure cylinder is used to transfer the mixed adhesive composition to a film, which is then laminated to a second film.

Preferably, phosphoric acid or a mixture of phosphoric acid and an epoxy resin is added to the composition to promote stability, improve adhesion and minimize viscosity build. Preferably the epoxy resin is a solid epoxy resin. Preferably, the phosphoric acid/epoxy resin mixture is added in an amount from 0.1 to 2 wt % of the combined components, preferably from 0.2 to 1.5 wt %, preferably from 0.3 to 1 wt %. Preferably, the phosphoric acid/epoxy mixture contains 5 to 40 wt % phosphoric acid, preferably 7 to 30 wt %, preferably 8 to 18 wt %. Preferably when phosphoric acid alone is added to promote stability, it is added in an amount from 0.01 to 2 wt % of the combined components, preferably from 0.03 to 1 wt %, preferably from 0.04 to 0.1 wt %. Preferably a solvent, e.g., ethyl acetate, is added to the mixture in an amount from 30-70 wt % of the total mixture including solvent.

The two-component urethane system is useful for bonding two to five substrates together. The substrates may be similar material or dissimilar material. Preferably, a layer of the bonding agent is applied to a first substrate layer, and the resulting bonding agent layer is covered with a second substrate layer to form a laminated article wherein the two substrates are bonded together by the dried layer of bonding agent. A third and fourth layer of film can be added to the laminate to form three- or four-layer laminates. Preferably, the substrate layers are provided in the form of rolls of substrate material. The sheets may be on the order of 0.5 to 10 mil in thickness. Larger thicknesses are also possible, as are smaller thicknesses (e.g., on the order of 5 or more microns).

The compositions of the present invention can be applied to desired substrates using conventional application techniques such as rotogravure printing, flexographic printing, conventional or airless spray, roll coating, brush coating, wire wound rod coating, knife coating, or coating processes such as curtain-, flood-, bell-, disc-, and dip-coating processes. Coating with the bonding agent may be done over an entire surface or only a portion of it, such as along an edge, or at intermittent locations. The bonding agent is particularly attractive for packaging and sealing applications for laminating plastic films, metal films or metallized plastic films. Especially preferred films include low density polyethylene, high density polyethylene, polypropylene (cast, blown oriented, biaxially drawn), nylon, polystyrene, co-extruded films, polyester film, ceramic (SiOx, AlOx) coated film (polyester, nylon, etc.), polyacrylic acid-coated film (polyester, nylon, etc.), polyvinylidene chloride coated film, metallized film (polyester, polypropylene, etc.).

Solution viscosities were measured using a Brookfield viscometer operating at a temperature of approximately 25° C. and with fittings appropriate for the viscosity ranges measured. Resin viscosities were measured on an ICI cone and plate viscometer at the plate temperatures indicated. Resins were prepared as described in the following procedures.